LJ  ; 

LO 


The 

Elizabethtown 

Bridge 


UN! 


H.  G.  TYRRELL 
Chief  Engineer 


The  Elizabethtown  Bridge 


Highway  Bridge 


over 


The  Miami  River 

at 

Elizabethtown,  Ohio 

The  Longest  Simple -Truss  Span 


Price  $1.00 


DESIGNED  BY 

H.  G.  TYRRELL,  CHIEF  ENGINEER 

AUTr*"*:  cr? 

MILL  E'J— -.. ,  3  JCTION, 


INTRODUCTION 


THIS   account   of  the   design    and   construction   of  the 
Elizabethtown  bridge,  has  been  prepared  in  response 
to   numerous   inquiries.      Several   years   have   elapsed 
since  the  bridge  was  completed  and  until  now  time  has 
not  permitted  me  to  write  any  description.     Brief  mention  of 
the  work  has  been  made  in  several  of  the  technical  journals, 
among  which  are  The  Iron  Age,  The  Canadian  Engineer,  The 
Railway  and  Engineering  Review,  and  others.    No  comprehen- 
sive description  has,  however,  appeared. 

Little  or  no  mention  is  made  in  this  description  of  the 
inspection,  tests  or  erection,  nor  is  there  any  sheet  of  details 
included. 

As  the  bridge  is  the  longest  truss  bridge  span  in  existence, 
it  will  continue  to  be  of  special  interest,  at  any  rate  until  such 
time  as  its  length  is  exceeded.  It  is  possible  that  at  some  future 
time,  the  account  may  be  revised  and  enlarged. 

H.  G.  TYRRELL. 

040  JUDSON  AVE. 
£YAJMSTON. 


Evanston,  Illinois,  February,  1909. 

240986 


Copyright,  1909,  by  H.  G.  Tyrrell 


Highway  Bridge  over  the  Miami  River 
at  Elizabethtown,  Ohio 

THIS  bridge  is  remarkable  in   being  the  longest  simple- 
truss  span  in  existence.    It  has  a  span  of  586  feet  be- 
tween centers  of  end  pins  and  surpasses  in  length  by 
36  feet  the  longest  other  span,  which  is  one  in  the 
bridge  crossing  the  Ohio  River  at  Cincinnati,  known  as  the 
Cincinnati  and  Covington  railway  and  highway  bridge. 

The  Old  Bridge.  On  the  site  of  the  present  new  steel  bridge, 
there  had  been  for  many  years  an  old  covered  wooden  bridge, 
known  locally  as  "Lost  Bridge."  It  consisted  of  three  spans, 
195  feet  long  each,  supported  on  stone  piers  and  abutments. 
The  old  piers  were  unusually  heavy,  and  yet,  notwithstanding 
this  fact,  the  foundation  beneath  them  was  badly  scoured,  so 
much  so  that  one  had  fallen  several  feet  out  of  plumb  at  the 
top.  The  superstructure  of  the  old  wooden  bridge  was  also 
rapidly  failing,  and  the  spans  showed  excessive  sag,  a  condi- 
tion frequently  developing  in  old  wooden  bridges  before  fail- 
ure. In  the  summer  or  autumn  of  1903  the  superstructure  of 
the  old  bridge  was  destroyed  by  fire,  and  the  need  of  replacing 
it  at  once  became  apparent. 

Type  and  Length  of  New  Bridge.  In  selecting  the  most  suit- 
able type  of  bridge  for  replacing  the  old  one,  there  were  numer- 
ous important  considerations.  The  rise  and  fall  of  the  water 
in  the  Miami  Eiver  is  very  uncertain.  At  flood  seasons  it  rises 
rapidly,  sometimes  20  feet  or  more  in  a  few  days.  The  greatest 
difference  between  high  and  low  water  is  about  30  feet.  At 
such  times  the  last  ten  feet  or  more  of  rise  is  back  water  from 
the  Ohio  River.  For  this  reason  all  bridges  in  this  district  are 
built  at  about  the  same  elevation  of  30  feet  above  low  water 
of  the  Ohio  River.  The  railroads  and  many  of  the  highways 


Description    of    High  way    Bridge 


are  likewise  built  on  banks  at  the  same  elevation,  for  at  Hood 
seasons  the  entire  country  around  is  liable  to  be  covered  with 
water. 

At  another  river  crossing,  about  a  mile  distant  from  Eliza- 
bethtown,  the  conditions  had  been  met  in  previous  years  by 
building  a  suspension  bridge  of  500  feet  clear  span,  spanning 
the  entire  width  of  the  water  course.  The  suspension  bridge 
is  quite  an  imposing  structure  and  an  ornament  to  the  district, 
but  is  lacking  in  the  more  important  requirement  of  rigidity. 
It  has  a  clear  roadway  of  20  feet  and  the  stone  towers  at  either 
end  are  placed  36  feet  apart,  so  the  cables  have  a  considerable 
cradle.  It  has,  also,  six  sets  of  stay  cables  from  the  towers 
to  the  floor,  and  is  braced  laterally  by  three  sets  of  rod  guys 
at  each  end,  fastened  to  stone  blocks  on  the  river  bank, 
yet  the  passage  of  ordinary  loads,  such  as  farm  wagons,  causes 
excessive  vibrations.  In  high,  or  even  moderate  winds,  the 
swaying  of  the  bridge  is  also  considerable. 

At  Xew  Baltimore,  Ohio,  in  the  same  county,  similar  condi- 
tions had  been  overcome  by  building  a  single  truss  span  465 
feet  in  length,  which  was  described  in  Engineering  News, 
October  16,  1902. 

The  railroads  were  also  having  difficulty  with  their  bridges 
in  the  same  region,  and  some  such  bridges  were  destroyed  by 
having  their  piers  undermined  by  the  scour  and  wash  of  the 
uncertain  currents  and  soil.  At  the  time  when  the  rebuilding 
of  the  Elizabethtown  bridge  was  being  considered,  a  railroad 
bridge  in  the  vicinity  was  being  strengthened  and  the  piers 
protected  at  great  expense,  by  having  large  quantities  of 
broken  stone  and  loose  rock  deposited  around  the  piers  and 
abutments.  It  was  found,  however,  that  notwithstanding  the 
dumping  in  of  many  carloads  of  rock,  and  the  strengthening 
of  piers  with  additional  concrete,  the  river  piers  were  still  in 
an  uncertain  condition  and  frequently  exposed  to  the  damag- 
ing influences  of  scour  and  the  shifting  of  the  channel. 

For  these  reasons  it  was  decided  to  avoid  the  use  of  river 
piers  in  rebuilding  the  bridge  at  Elizabethtown,  and  to  bridge 
the  entire  waterway  with  a  single  span.  Having  thus  decided 
on  the  use  of  a  single  span,  approximating  600  feet  in  length. 


at   Elizabethtoicn,    Ohio 


it  then  became  necessary  to  select  the  most  suitable  type  of 
bridge. 

The  suspension  bridge  described  above  is  in  some  respects 
very  desirable,  but  on  account  of  its  lack  of  stiffness  was  not 
seriously  considered  as  a  type  for  Elizabethtown.  The  under- 
neath clearance  would  not  permit  the  use  of  a  deck  arch  of 
so  long  a  span,  and  a  through  arch,  such  as  those  used  at 
Bonn  or  Dusseldorf,  or  more  recently  at  Bellows  Falls,  Ver- 
mont, are  lacking  in  lateral  stiffness.  In  through  arches  such 
as  those  mentioned  above,  it  is  necessary,  in  order  to  maintain 
the  required  clearance  through  the  bridge,  to  omit  top  lateral 
bracing  between  the  arch  ribs  for  some  considerable  distance 
back  from  the  springs.  This  is  more  serious  than  in  truss 
bridges,  where  the  end  posts  incline  at  an  angle  of  45  degrees 
or  more  with  the  horizontal.  With  the  through  arch  the  slope 
of  the  ribs  is  so  gradual  that  a  large  part  of  the  most  effective 
lateral  bracing  between  the  ribs  must  necessarily  be  omitted. 

Some  forms  of  stiffened  suspension  bridge,  and  a  cantilever 
design  of  600  feet  span  between  piers,  with  back  stays  similar 
to  the  back  stays  of  a  suspension  bridge,  were  also  considered. 
None  of  these  forms  were  favored,  chiefly  because  of  their  lack 
of  stiffness.  Of  the  alternate  forms  considered,  the  cantilever 
above  referred  to  would  doubtless  have  given  the  best  results. 
It  would  leave  the  waterway  entirely  free  of  piers  and  would 
permit  the  use  of  a  narrower  roadway,  by  placing  the  trusses 
further  apart  at  the  shore,  than  at  the  end  of  the  cantilever 
arms.  It  is  interesting  to  note  that  a  bridge  of  this  type  has 
since  been  built  at  Long  Lake,  N.  Y.,  and  is  described  in  the 
Engineering  Record  of  September  29,  1906. 

After  due  consideration  of  various  types,  it  was  decided  to 
use  a  through,  pin  connected,  simple-truss  bridge. 

Invitation  for  Tenders.  The  bridge  was  being  built  by  Ham- 
ilton County,  and  advertisements  were  therefore  printed,  call- 
ing for  separate  tenders  for  substructure  and  superstructure. 
The  advertisement  gave  the  length  of  span  as  586  feet  between 
centers  of  truss  bearings  and  called  for  competitive  plans  and 
bids  to  be  submitted. 


10  Description    of   Highway   Bridge 

Substructure  Tenders.  In  response  to  the  advertisements, 
tenders  for  building  and  repairing  the  substructure  were  re- 
ceived from  five  competing  firms,  which  are  given  below: 


No.  1        No.  2         No.  3         No.  4        No.  5 
Forming  bank,  cu.  yd.  .$        .35    $        .30    $        .40    $        .40   $        .38 


Excavation,  per  cu.  yd. 

1.50 

.90 

1.00 

1.00 

.90 

Crushed  stone,  pr  cu.yd. 

1.80 

1.20 

1.80 

1.80 

1.75 

Screenings,  per  cu.  yd. 

1.80 

1.20 

1.80 

1.80 

1.75 

Lumber    per  M  .  .  

60.00 

40.00 

50.00 

40.00 

40.00 

Rolling,  per  sq.  yd  .  .  .  . 

.05 

.01 

.05 

y 
.05 

.05 

Piling    per  lin    ft 

.50 

.37 

.50 

.30 

.50 

Concrete,  per  cu.  yd.  .  . 

9.00 

10.00 

8.00 

8.00 

8.00 

Sheet  piling,  per  M.  .  .  . 

15.00 

10.00 

15.00 

13.00 

12.40 

Bridge  seat  beams  .... 

1500.00 

1000.00 

1495.00 

600.00 

1500.00 

Steel  rods    per  Ib 

.04 

.035 

.05 

.03 

.045 

Puddling,  per  cu.  yd.  .  . 

2.00 

2.00 

2.00 

2.00 

2.00 

The  foundation  work  consisted  chiefly  in  repairing  the  old 
stone  abutments  by  building  up  new  material  in  reinforced 
concrete  in  front  of  the  old  stone  work,  carrying  up  the  retain- 
ing walls  and  parapets,  and  rebuilding  the  bridge  seats  with 
lines  of  steel  beams  embedded  in  concrete. 

As  this  part  of  the  work  presented  no  unusual  difficulty,  or 
was  not  of  particular  interest,  details  of  the  substructure  are 
not  given.  It  will  be  interesting,  however,  to  note  that  the 
presence  of  the  old  piers  was  some  considerable  assistance  dur- 
ing erection.  The  steel  work  was  assembled  and  erected  on 
timber  false  work  at  low  water  season. 

Superstructure  Tenders.  Competitive  plans  and  prices  were 
received  from  eighteen  different  firms  for  the  design,  con- 
struction and  erection  of  the  superstructure,  with  the  result 
that  the  design  prepared  by  the  writer  was  accepted  and  the 
contract  was  awarded  accordingly. 

Description  of  Accepted  Design.  In  preparing  a  design  sev- 
eral comparative  estimates  were  made,  differing  principally 
in  the  depth  of  truss,  number  of  panels,  design  of  floor  system, 
and  live  loads.  A  summary  of  these  estimates  is  as  follows : 


at   Elizabethtown,    Ohio 


11 


Comparative  Estimates  for  Elizabethtown  Bridge, 


Plan 

No.  of   Width  of 
Panels    Road 

Dead  Load 
Joist                    per  ft. 

Live  Load 
per  ft 

Steel 
tons 

Estimated 
Cost 

Cost 
plus  25% 

A 

22 

30' 

10 

"  I's 

2'  apart 

3,480 

2,400 

920 

$68,000 

$85,000 

B 

22 

30' 

12 

"  I's 

3'  apart 

2,710 

1,200 

686 

53,000 

66,200 

C 

18 

30' 

7 

"  I's 

3'  apart 

2,304 

1,000 

560 

39 

,700 

49,500 

D 

18 

30' 

3 

"x!4" 

3'  apart 

2,122 

1,000 

514 

37 

,700 

47,100 

E 

18 

30' 

15 

"  I's 

5'  apart 

2,358 

1,000 

554 

39 

,600 

49,400 

F 

18 

30' 

15 

"  I's 

3'  apart 

2,442 

1,000 

604 

41 

,900 

52,400 

G 

24 

30' 

10 

"I's 

3'  apart 

2,438 

1,000 

607 

42 

,800 

53,500 

H 

24 

30' 

12 

"I's 

5'  apart 

2,488 

1,000 

591 

42 

,oOO 

53,100 

K 

24 

30' 

6 

"I's 

3'  apart 

2,445 

1,000 

601 

43 

,400 

54,200 

L 

18 

30' 

7 

"I's 

2.5'  ap't 

2,590 

1,000 

643 

45 

,200 

56,500 

M 

24 

35' 

10 

"  I's 

3'  apart 

3,500 

1,500 

867 

68 

,900 

86,100 

N 

24 

35' 

3,144 

1,000 

769 

60 

,900 

76,100 

O 

18 

35' 

6 

"I's 

3'  apart 

3,09*2 

1,400 

713 

57 

,300 

71,600 

P 

24 

30' 

10 

"  I's 

2'  apart 

2,825 

1,000 

710 

50,400 

63,000 

The  center  truss  depth  in  all  designs  from  A  to  L,  inclusive, 
was  80  feet ;  also  for  design  P ;  while  M  and  N  are  87  feet,  and 
O,  75  feet  deep. 

In  designs  K,  L  and  O,  it  will  be  seen  that  six-  or  seven-inch 
steel  joist  are  used,  while  in  all  other  designs  much  larger 
beams  are  required.  The  ability  to  use  smaller  joist  is  plainly 
due  to  the  shorter  panels  of  the  floor  system.  Comparative 
estimates  were  made  to  ascertain  the  relative  economy  between 
using  a  larger  number  of  short  truss  panels  and  a  smaller 
number  of  longer  truss  panels,  with  intermediate  floor  beams 
in  each  panel,  carried  on  heavy  side  girders.  The  comparisons 
clearly  showed  the  economy  of  longer  truss  panels.  Design  L 
was  therefore  selected  as  providing  the  economy  of  long  panels 
in  the  trusses  and  at  the  same  time  short  panels,  and  corre- 
spondingly small  joist  for  the  floor  system.  Diagrams  7  to  12 
inclusive,  illustrate  the  various  designs  considered  by  the 
writer,  No.  12  being  the  selected  one,  and  the  outline  on  which 
the  bridge  is  built.  The  width  selected  for  the  roadway  was 
30  feet,  and  as  the  end  posts  and  top  chords  are  30  inches  wide, 
the  distance  between  centers  of  trusses  is  32  feet  6  inches, 
which  is  one-eighteenth  of  the  entire  span.  The  trusses  are 


12  Description   of   Highway   Bridge 

divided  into  18  panels,  32  feet  6  inches  long  each,  making 
square  panels  for  the  lateral  system.  The  type  of  truss  is  the 
subdivided  Pratt,  with  main  panels  65  feet  long.  The  depth 
of  truss  varies  from  80  feet  at  the  center  to  40  feet  at  the  first 
panel  point.  The  curve  of  the  top  chord  is  a  parabola,  in 
straight  sections  of  two  panel  length.  Stiff  laterals  and  sway 
bracing  are  used  throughout.  This  is  a  very  essential  feature 
of  the  design,  and  one  upon  which  much  of  the  stiffness  of  the 
bridge  depends.  Lateral  and  other  light  struts  are  built  in 
box  form,  latticed  on  all  four  sides.  The  first  panel  of  diag- 
onals in  the  top  lateral  system  are  built  in  the.  same  way.  Each 
of  the  32-feet-6-inch  panels  of  the  floor  system  are  again  sub- 
divided by  carrying  an  intermediate  floor  beam  on  two  longi- 
tudinal beams,  one  at  each  side  of  the  bridge.  In  addition  to 
the  benefit  of  economy  in  floor  framing,  the  two  side  beams 
serve  also  as  chords  for  the  lower  lateral  system.  The  longi- 
tudinal and  cross  floor  beams  are  of  the  same  size,  and  diagonal 
laterals  are  rigidly  connected  by  plates,  which  fasten  to  the 
bottom  flanges  of  both  cross  and  longitudinal  beams.  The 
floor  joist  consist  of  6-inch  steel  beams,  spaced  2  feet  6  inches 
apart,  elevated-on  9-inch  beam  corbels.  On  the  steel  joist  is  laid 
the  2%-inch  oak  flooring,  spiked  to  six  lines  of  3x7  oak  spiking 
pieces,  with  60d  nails.  The  wheel  guards  are  6x6-inch  oak, 
beveled  on  the  inner  edge  and  elevated  on  4  inch  blocks,  spaced 
2  feet  apart  for  drainage.  The  bridge  was  given  an  initial 
camber  at  the  center  of  3  feet.  On  each  side  of  the  roadway 
there  is  a  neat  railing,  made  of  four  angles  latticed  in  box  form. 
This  railing  lines  up  with  the  inner  face  of  the  web  posts  and 
fastens  to  them.  The  portal,  as  shown  on  the  writer's  design, 
is  a  heavy  lattice  framework,  but  it  was  changed  in  the  shop 
to  one  of  plate  construction.  This  change  was  plainly  a  mis- 
take, as  it  does  not  in  any  way  harmonize  with  the  light  fram- 
ing of  the  bridge.  The  lack  of  harmony  of  the  portal  with  the 
rest  of  the  bridge  shows  very  clearly  in  the  photographic  view. 
The  two  side  lines  of  heavy  floor  stringers,  which  act  also  as 
wind  truss  chords,  are  rigidly  attached  by  means  of  bottom 
bracket  angles  to  the  main  truss  posts.  Such  portions  of  the 
wind  chord  stresses  as  are  not  resisted  by  these  longitudinal 


at   Elizabethtoicn.    Ohio 


13 


side  beams,  are  transferred  to  the  bottom  chord  eye  bars, 
through  these  rigid  connections. 

The  cross  beams,  at  the  panel  points,  are  suspended  by  two 
rod  hangers  1%  inches  in  diameter  each,  from  the  bottom 
chord  pins,  and  at  the  same  time  they  are  riveted  to  the  bottom 
angles  on  the  web  posts.  This  gives  a  rigid  floor  beam  connec- 
tion and  at  the  same  time  reduces  the  cost  of  erection.  At 
one  end  of  the  bridge  are  sets  of  turned  rollers,  and  at  both 
ends  the  heavy  side  beams  are  connected  to  the  shoe  boxes, 
thereby  transferring  the  wind  strains  as  directly  as  possible 
to  the  masonry.  The  vertical-  posts  are  spliced  at  the  joints 
of  the  lateral  struts.  The  minimum  thickness  of  metal  used  is 
one-quarter  inch. 

The  metal  throughout  is  medium  steel  of  60,000  to  68,000 
pounds  per  square  inch  tensile  strength,  conforming  to  the 
Manufacturers'  Standard  Specifications. 

The  following  is  a  detail  estimate  of  the  material  in  the 
superstructure : 


Steel 

Steel 
pounds 

Pounds 
per  lin.  ft. 

Joist 

185  000 

315 

Floor  beam  and  hangers  

83,000 

142 

Bracing 

203  000 

345 

Railing 

20  500 

35 

Shoes   

24  000 

41 

Trusses    .     ... 

769  000 

1  312 

Total  steel     ... 

1  284  500 

2  190 

Lumber     

54  000   feet    board 

measure 

Loads.  The  assumed  dead  load  per  lineal  foot  of  bridge 
used  in  determining  the  stresses,  was  2,900  pounds.  This  in- 
cludes the  weight  of  all  steel  and  lumber,  and  300  pounds  per 
lineal  foot  for  snow  and  ice.  The  snow  load  causes  no  vibration 
or  impact  and  was  therefore  classed  as  dead  load.  The  effect 
however  on  the  web  members  of  a  partial  snow  load,  was  con- 
sidered and  provided  for.  Wet  lumber  was  assumed  to  weigh 
seven  pounds  per  foot  board  measure.  Seven-tenths  of  the 


r  >•* 


§ 

* 

N 

Q 


16  Description   of   Highway   Bridge 

entire  dead  load  was  assumed  as  acting  at  points  of  the  bottom 
chord,  and  the  remaining  three-tenths  at  the  points  of  the  top 
chord. 

The  assumed  live  load  was  1,000  pounds  per  lineal  foot  of 
bridge,  for  the  trusses,  and  for  the  floor  and  its  supports  70 
pounds  per  square  foot  of  roadway,  or  a  ten  ton  road  roller  or 
wagon.  These  loads  are  all  in  addition  to  the  weight  of  snow 
and  ice  as  described  above. 

The  wind  load  was  taken  at  30  pounds  per  square  foot  of 
exposed  surface. 

After  the  completion  of  the  bridge  it  was  the  intention  to 
remove  the  two  river  piers,  one  of  which  was  already  leaning 
over  and  in  danger  of  falling. 

The  accompanying  stress  sheet  shows  the  maximum  stresses 
in  the  various  members  for  dead,  live  and  wind  loads,  and  the 
sizes  and  sections  used.  The  coefficient  diagrams  show  the 
stress  in  the  various  members  for  panel  loads  of  unity. 

Competitive  Designs.  Diagrams  Nos.  1  to  6,  inclusive,  show 
the  truss  outlines  for  some  of  the  designs  submitted  by  other 
engineers  and-  bridge  companies.  All  outlines  having  22  panels 
or  more  in  the  trusses  have  evidently  an  excessive  number  of 
web  members  for  economy.  Number  5  has  too  shallow  a  truss, 
while  No.  6  is  too  deep.  Number  6,  with  panels  48  feet  in 
length,  was  designed  for  a  heavy  system  of  floor  framing, 
somewhat  similar  to  the  accepted  design  No.  12,  excepting  that 
in  place  of  rolled  beams  for  the  main  floor  supports,  plate 
girders  were  used.  Each  panel  then  became  a  plate  girder  span 
48  feet  in  length  and  30  feet  in  width,  with  several  intermediate 
floor  beams  carried  on  the  heavy  side  plate  girders,  the  cross 
floor  beams  supporting  steel  joist.  The  weight  of  the  floor  system 
in  No.  6  is  excessive,  due  to  the  unusual  length  of  truss  panels. 
Those  truss  outlines  have  a  better  appearance  where  the  curve 
of  the  top  chords  is  uniform  from  end  to  end  between  the  upper 
ends  of  end  posts.  The  break  in  this  curve  at  the  second 
panel  points  in  the  upper  chord,  as  shown  in  diagram  No.  2,  is 
unsightly.  Number  5  has  the  appearance  of  being  too  flat  over 
the  central  panels  of  the  top  chord. 


at   Elizabethtoicn,    Ohio 


17 


Table  of  Long  Span  Bridges 

For  the  purpose  of  comparison,  a  table  of  other  long  span 
bridges  is  given,  arranged  in  the  order  of  their  length. 


River 


Date 


Location 


Kind  of  Bridge      Span 
Railway  or  highway    ft. 


Engineer 


1904 

Elizabethtown 

Miami 

Highway 

586 

H.  G.  Tyrrell 

1888 

Cincinnati 

Ohio 

Railway  and 

550 

Wm.  H.  Burr 

Highway 

1894 

Louisville 

Ohio 

Railway 

546 

Phoenix  Bridge  Co. 

1889 

Cincinnati 

Ohio 

Railway  and 

542 

Highway 

1896 

Philadelphia 

Delaware 

Railway 

533 

1890 

Pittsburg 

Ohio 

Railway 

523 

St.  Louis 

Mississippi 

Railway 

524 

1885 

Henderson 

Ohio 

Railway 

522 

Keystone  Bridge  Co. 

1889 

Ceredo 

Ohio 

Railway 

521 

T.  K.  Thomson 

Cairo 

Ohio 

Railway 

520 

Union  Bridge  Co. 

Havre  de  Grace 

Susquehanna 

Railway 

515 

1877 

Cincinnati 

Ohio 

Railway 

515 

J.  H.  Linville 

1870 

Kuilenburg 

Leek  River 

515 

G.  Van  Diesen 

1902 

New  Baltimore 

Miami 

Highway 

465 

J.  H.  Hilton 

1859 

Saltash 

Taular 

Railway 

456 

Brunei 

1889 

Hawksbury 

Railway 

416 

Union  Bridge  Co. 

1901 

Hamilton 

Miami 

Highway 

406 

The  Miami  empties  into  the  Ohio  River  below  the  City  of  Cin- 
cinnati. It  will  be  seen  that  many  of  the  longest  spans  are  over 
the  Ohio  and  its  tributaries.  In  the  tributaries  near  their  mouth 
the  high  water  conditions  are  similar  to  those  of  the  Ohio  River 
itself. 

Superstructure  Specifications. 

The  following  are  extracts  from  the  general  specifications 
under  which  the  bridge  was  built : 

1.  Headroom. — The  bridge  shall  have  a  clear  headroom  of 
not  less  than  14  feet. 

2.  Material. — All  framing  of  the  bridge  shall  be  made  of 
wrought  steel,  of  the  grade  known  as  Medium  Steel,  with  an 
ultimate  tensile  strength  of  from  60,000  to  68,000  pounds  per 


Z  8 


22 


2o 


2o 


X  ««  > 

7X7 


/  8 


2  2 


22 


/  8 


20  Description    of    Highway    Bridge 

square  inch,  and  an  elastic  limit  of  not  less  than  one-half  the 
ultimate  strength. 

3.  Flooring. — The  flooring  shall  consist  of  a  single  thickness 
of  oak  plank,  laid  crosswise  of  the  bridge  and  at  right  angles 
to  the  center  line.    It  shall  be  laid  in  two  lengths,  meeting  at 
the  center,  where  it  shall  be  spiked  to  two  lines  of  wood  joist, 
and  the  joints  in  the  plank  flooring  covered  by  a  longitudinal 
oak  timber,  dividing  the  width  of  the  bridge  into  two  separate 
driveways.    The  plank  shall  have  a  thickness  not  less  than  one- 
twelfth  of  the  distance  between  joists.     At  either  side  of  the 
bridge  there  shall  be  oak  wheel  guards  not  less  than  4x6  inches, 
set  up  on  oak  blocks  spaced  not  more  than  five  feet  apart. 
These  wheel  guards  shall  be  bolted  securely  through  the  floor- 
ing with  iron  bolts  with  washers. 

4.  Loads. — In  addition  to  the  dead  load  of  material  in  the 
bridge,  it  shall  be  proportioned  to  sustain  a  moving  live  load 
of  1,000  pounds  per  lineal  foot  of  bridge  and  an  additional 
load  of  300  pounds  per  foot  for  snow  and  ice.    This  latter  may 
be  considered-  as  dead  load.     The  structure  shall  be  propor- 
tioned for  a  wind  load  of  30  pounds  per  square  foot,  acting  on 
the  exposed  surface  of  both  trusses,  and  all  bracing  that  is 
likewise  exposed  to  wind  pressure. 

5.  Unit  Stresses.     The  permissible  unit  stresses  shall  be  as 
follows : 


Pounds 
per  sq.  ft. 

Tension: 

(  minimum 
Tension  in  eye  bars 12,000  ]  I— 

(  maximum 
Tension  in  laterals 20,000 

Tension  for  combined  dead,  live  and  wind 

loads 25,000 

Tension  in  bottom   flanges   of  solid   rolled 

beams  .  12,500 


at   Elizabethtown,    Ohio  21 


Pounds 
per  sq.  in. 

Compression : 

L 

Lateral   struts P=13,000  -    60  - 

r 

L 

Chords,  live  loads P— 12,000  -    55  - 

r 

L 

Chords,  dead  loads P— 24,000  -  110  - 

r 

L 
Web  posts,  live  loads P=10,000  -  45  - 

r 

.  L 

Web  posts,  dead  loads P=20,000  -  90  - 

r 


In  the  above,  P  is  the  allowable  stress  per  square  inch  in  pounds. 
L  is  the  length  of  member  in  inches, 
r  is  the  least  radius  of  gyration  in  inches. 

No  compression  member  shall  have  a  length  exceeding  100 
times  its  least  radius  of  gyration  for  main  members,  or  120  times 
for  lateral  struts. 

The  maximum  allowable  shearing  stress  on  rivets,  bolts  and 
pins  shall  not  exceed  10,000  pounds  per  square  inch,  the  bear- 
ing stress  shall  not  exceed  20,000  pounds  per  square  inch,  and 
the  bending  stress  25,000  pounds  per  square  inch.  Connections 
for  field  rivets  shall  have  25  per  cent  more  rivets  than  required 
by  the  above  allowable  units  for  shop  rivets. 

6.  Details  of  Construction. — Eye  bars  shall  be  so  made  that 
in  testing  they  shall  break  in  the  body  of  the  bar  rather  than 
in  the  head.  Welding  will  not  be  allowed  in  the  body  of  the 
bar.  Holes  shall  be  bored  in  the  center  of  the  head,  and  on 
the  center  line  of  the  bar. 

All  bracing  throughout  shall  be  capable  of  resisting  both 
tension  and  compression.  In  proportioning  the  sizes  for  lateral 
bracing,  both  systems  shall  be  considered  acting  at  the  same 
time,  the  compression  pieces  resisting  up  to  their  safe  capacity, 
and  the  balance  of  stress  being  carried  by  the  tension  member. 


22  Description    of    Highway    Bridge 

The  upper  lateral  struts  shall  be  the  full  depth  of  upper  chord 
and  shall  be  rigidly  attached  thereto.  The  lower  lateral  diag- 
onals shall  be  connected  at  the  panel  points  of  the  truss  so  that 
stress  components  from  the  lateral  system  shall  be  transmitted 
to  the  main  truss  chords.  The  floor  beams  shall  be  so  attached 
that  there  will  be  no  tendency  towards  rotation  about  the  chord 
pins. 

Overhead  cross  sway  bracing  shall  be  placed  at  the  truss 
panels  and  this  shall  be  as  deep  as  head  room  or  proper  truss 
connections  will  permit.  It  shall  be  all  stiff  bracing,  and  where 
necessary,  provision  shall  be  made  in  the  vertical  chord  posts 
and  suspenders,  to  resist  bending  stresses  from  the  sway  brac- 
ing. 

End  portals  shall  be  as  deep  as  the  necessary  clearance  will 
permit.  They  shall  be  rigidly  attached  to  the  end  posts  and 
upper  chords,  and  proper  provision  shall  be  made  in  the  sec- 
tions of  the  end  posts  to  resist  the  bending  therein  due  to  the 
action  of  the  portal  in  transmitting  stresses  from  the  upper 
lateral  system  to  the  abutments. 

Counters  shall  be  proportioned  considering  that  only  70  per 
cent  of  the  dead  load  stress  in  the  main  member  acts  in  neutral- 
izing or  counteracting  the  live  load  stress  in  the  counter. 

Long  vertical  tension  members  shall  preferably  be  stiffened. 

Riveted  tension  members  connected  to  pins,  shall  have  an 
excess  of  area  through  the  pin  holes  of  25  per  cent  over  the 
section  of  the  main  part. 

Provision  for  expansion  shall  be  made  to  the  extent  of  one 
inch  for  every  one  hundred  feet  of  span.  There  shall  be  at  one 
end  sets  of  expansion  rollers  not  less  than  two  and  one-half 
inches  in  diameter,  on  which  the  pier  boxes  shall  rest. 

Bed  plates  and  pier  boxes  shall  be  sufficiently  large  that  the 
pressure  on  masonry  will  not  exceed  400  pounds  per  square 
inch. 

Splices  in  compression  members  shall  have  an  absolutely 
even  bearing,  and  shall  be  milled  or  planed.  They  shall  have 
the  necessary  amount  and  number  of  splicing  plates  to  properly 
and  securely  hold  the  sections  in  position. 


II.  G.  TYRRELL,  CIVIL  ENGINEER 

Chicago,  Illinois 
Evanston,  Illinois 

Designer  and  Engineer  for  All  Kinds  of 
Bridges  and  Structures 

Special  Attention  to  Selection 
of  Economic  Types 

Phone  3231 


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